Thin metallic and ceramic layers may be deposited upon a substrate by a process known as magnetron sputtering. In such a process, a sputtering target assembly is used that has a target surface of the material to be deposited. Magnetron sputtering and target assemblies used for sputtering, are well known.
Sputtering target assemblies typically include a target member supported on the backing plate. The target member includes a target surface of material to be sputtered. The backing member is intended to secure the target in place in a sputtering apparatus. Conventional methods of manufacturing target assemblies have included bonding a target member to a backing plate by TIG welding, brazing, soldering, and explosion bonding. TIG welding, brazing and explosion bonding are not low-temperature processes as is solder. They are, therefore, not subject to any temperature limitations on the target. TIG welding (or e-beam welding) have disadvantages of potential leaks and possible particle generation during sputtering and, in any case, these types of targets are typically not weldable. Explosion bonding is considered to be too expensive to be cost-effective. However, solder alloys typically used for joining the target to the backing plate by such methods have relatively low melting points and, therefore, cannot withstand high temperatures. The manufacturing cost of making conventional sputtering target assemblies is relatively high because of the many steps of the manufacturing process and the equipment required.
It is desirable to provide a more economical method of making sputtering target assemblies than the methods described above. It is also desirable to produce target assemblies capable of sputtering use at higher power levels than at which solder-bonded assemblies can be used to enable higher throughput of the sputtering process which, in turn, reduces cost of manufacturing articles that employ sputtering in their manufacture.
To avoid solder bonding, sputtering target assemblies can be advantageously made by powder metallurgical processes. One such process is disclosed in Mueller, U.S. Pat. No. 5,397,050, dated Mar. 14, 1995, which describes a method of producing a sputtering target assembly consisting of a tungsten-titanium alloy target attached to a titanium backing plate wherein a can containing a tungsten-titanium powder is consolidated to form a target. The can containing the powder is hot isostatic pressed to a titanium backing plate to form an interdiffusion-type bond between the target and the backing plate. However, since the process involves hot isostatic pressing powder contained within a can, it is relatively costly due to the use of expensive machining, canning and hot isostatic pressing procedures and equipment which add to manufacturing cost. In addition, because of the use of cannage there is a risk of entrapping gas which can cause voids in the product.
The present invention provides an efficient and relatively low cost method of producing sputtering target assemblies from powdered material by hot pressing without use of a container format so that gases are not entrapped. The method produces a sputtering target assembly with lower gas content and lower void levels which, in turn, results in lower particulate defects in the article, e.g., wafer, on which the sputtered material is deposited.